page_title: Work (thermodynamics)
section_title: 1845
hierarchical_section_title: Work (thermodynamics) / History / 1845
caption_attribution_description: English: Engraving of James Joule's apparatus for measuring the mechanical equivalent of heat, in which altitude potential energy from the weight on the right is converted into heat at the left, through stirring of water. Français&#160;: Gravure représentant l’installation expérimentale utilisée par James Joule pour mesurer l’équivalence entre chaleur et travail. L’énergie potentilelle d’altitude du poids, à droite, est convertie en chaleur par agitation de l’eau à gauche.
context_page_description: In thermodynamics, work transfer is an energy transfer in which temperature is not considered during energy transfer. Unit is always in Joules. It is also a result of force acting through the distance. W=FxD
context_section_description: In 1845, the English physicist James Joule wrote a paper On the mechanical equivalent of heat for the British Association meeting in Cambridge. In this work, he reported his best-known experiment, in which the work released through the action of a "weight falling through a height" was used to turn a paddle-wheel in an insulated barrel of water.
  In this experiment, the friction and agitation of the paddle-wheel on the body of water caused heat to be generated which, in turn, increased the temperature of water.  Both the temperature change ∆T of the water and the height of the fall ∆h of the weight mg were recorded.  Using these values, Joule was able to determine the mechanical equivalent of heat. Joule estimated a mechanical equivalent of heat to be 819 ft•lbf/Btu (4.41 J/cal).  The modern day definitions of heat, work, temperature, and energy all have connection to this experiment.
caption: Joule's apparatus for measuring the mechanical equivalent of heat.
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